The lifespan of a structure is often dictated by the magnitude of strain applied to the structure. Strain or relative peak deflection in a structural material or system may cross a predetermined safety threshold and indicate the material or system should be removed from service, or that maintenance must be performed to ensure continued integrity. Thus, accurate peak strain measurements for a structure are important.
It will be understood that the term "strain gauge" as used herein refers to both strain and deflection gauges. Strain gauges are divided into passive and active categories. Passive strain gauges include a passive deflection sensor and generally measure strain only at the sampled time. Thus, if the member is not undergoing the peak strain when the passive strain gauge is activated, the peak strain is not measured. Active strain gauges avoid this limitation by using a deflection sensor coupled with an on-site microprocessor constantly running to measure and store into an electronic memory the instantaneous deflection of a structural member. Peak strain is determined by reviewing the stored deflection information. However, active strain gauges are more complicated, fragile and expensive than passive strain gauges due to the incorporation of the microprocessor and memory components.
What is needed is a passive strain gauge that more accurately retains its state caused by peak strain or deflection for later measurement.